This invention relates to a method for determining the combustion condition that is capable of determining rapidly and exactly the combustion condition in a spark ignition internal combustion engine by detecting physical phenomena directly relating to the combustion, and to a combustion condition control device that is capable of controlling the combustion condition in the engine rapidly and correctly.
Normal combustion in a spark ignition internal combustion engine proceeds in such a manner that part of fuel mixture is ignited by a spark from an ignition plug, and the flame propagates into the fuel mixture. However, knocking occurs when part or all of the uncombusted mixture self-ignites at a time before the propagation of the flame, caused by an increase in temperature due to compression of the mixture. Since a rapid increase in pressure in the combustion chamber associated with this violent combustion and the propagation of a pressure wave cause mechanical vibrations in engine parts and overheat of ignition plugs and pistons, knocking is one of the most harmful phenomena in a spark ignition internal combustion engine.
However, the ignition timing for the spark ignition internal engine (hereinafter simply referred to as "engine") to generate a maximal torque, as well known, is in the vicinity of knocking conditions, the ignition timing condition for the maximal torque tends to have a high probability of knocking.
Heretofore, the engine has been provided with a cylinder internal pressure sensor or an acceleration sensor to detect vibrations in the cylinder or accelerations generated in the engine that occur in association with knocking, thereby evaluating the operation conditions or ignition timing, or correcting the ignition timing during operation to suppress occurrence of knocking while obtaining a maximal torque from the engine.
However, with the prior art method in which vibrations in the cylinder internal pressure or accelerations in the engine unit are sensed by a cylinder internal pressure sensor or an acceleration sensor, knocking cannot be detected unless it actually occurs in the engine, and it has been substantially impossible to detect a condition immediately before the occurrence of knocking to prevent knocking from occurring or to determine the allowance to knocking. Furthermore, such a cylinder internal pressure sensor tends to sense mechanical vibrations and cause mis-detection.